c16 energetics

• Exothermic


  Energy released into surrounding, related to increase in temperature of surrounding
• Exothermic reaction


  • Energy level of reactants > energy level of products
  • Energy absorbed to break bonds in reactants < energy released to form bonds in products
  • Bond making releases energy to surroundings
• Activation energy (Ea)


  Minimum amount of energy that colliding particles must possess to react with each other
• Collision energy < Ea


  Particles do not react
• Collision energy ≥ Ea


  Reaction occurs, product molecules formed
• Endothermic reaction


  • Energy level of reactants < energy level of products
  • Energy absorbed to break bonds in reactants > energy released to form bonds in products
  • Bond breaking requires energy, absorbed from surroundings
• Enthalpy change (ΔH) = Total energy of products - Total energy of reactants
• Enthalpy change (ΔH) has units of kJ/mol, negative value means exothermic, positive value means endothermic
• Bond energy


  Amount of energy absorbed to break one mole of a chemical bond, and amount of energy released when one mole of that bond is formed
• Physical changes that are exothermic

  • Condensation
  • Freezing
  • Vapour deposition
  • Dissolving of anhydrous salts
  • Dissolving of acids in water
• Chemical reactions that are exothermic

  • Combustion of fuels
  • Respiration
  • Neutralisation
• Physical changes that are endothermic

  • Evaporation
  • Melting
  • Sublimation
  • Dissolving of some ionic compounds
• Chemical reactions that are endothermic

  • Photosynthesis
  • Thermal decomposition